Benign prostatic hyperplasia (BPH) is a common disorder in middle-aged and older men, with prevalence increasing with age. At age 70, more than one-half of men have symptomatic BPH, and nearly 90% of men have microscopic evidence of an enlarged prostate. The severity of symptoms also increase with age with 27% of patients in the 60-70 age bracket having moderate-to-severe symptoms, and 37% of patients in their 70's suffering from moderate-to-severe symptoms.
The prostate gland early in life is the size and shape of a walnut and weighs about 20 grams. Prostate enlargement appears to be a normal process. With age, the prostate gradually increases in size to twice or more its normal size. The fibromuscular tissue of the outer prostatic capsule restricts expansion after the gland reaches a certain size. Because of such restriction on expansion, the intracapsular tissue will compress against and constrict the prostatic urethra thus causing resistance to urine flow.
FIG. 1 is a sectional schematic view the male urogenital anatomy, with the walnut-sized prostate gland 50 located below the bladder 55 and bladder neck indicated at 56. The walls 58 of bladder 55 can expand and contract to cause urine flow through the urethra 60, which extends from the bladder 55, through the prostate 50 and penis 62. The portion of urethra 60 that is surrounded by the prostate gland 50 is referred to as the prostatic urethra 70. The prostate 50 also surrounds the ejaculatory ducts 72 which have an open termination in the prostatic urethra 70. During sexual arousal, sperm is transported from the testes 74 by the ductus deferens 76 to the prostate 50 which provides fluids that combine with sperm to form semen during ejaculation. On each side of the prostate, the ductus deferens 76 and seminal vesicles 77 join to form a single tube called an ejaculatory duct 72. Thus, each ejaculatory duct 72 carries the seminal vesicle secretions and sperm into the prostatic urethra 70.
Referring to FIGS. 2A-2B and 3, the prostate glandular structure can be classified into three zones: the peripheral zone PZ, transition zone TZ, and central zone CZ. FIGS. 2A and 2B illustrate a normal prostate gland, and FIG. 3 schematically depicts an enlarged prostate resulting from benign prostatic hyperplasia. FIGS. 2A-2B and 3 include reference to other male anatomy as previously described with respect to FIG. 1. In a normal prostate as depicted in FIGS. 2A-2B, the peripheral zone PZ, which is the region forming the postero-inferior aspect of the gland, contains 70% of the prostate glandular elements. A majority of prostate cancers (up to 80%) arise in the peripheral zone tissue PZ. The central zone CZ surrounds the ejaculatory ducts 72 and contains about 20-25% of the prostate volume in a normal prostate. The central zone is often the site of inflammatory processes. The transition zone TZ is the site in which benign prostatic hyperplasia develops, and contains about 5-10% of the volume of glandular elements in a normal prostate (FIGS. 2A, 2B). Referring to FIG. 3, the peripheral zone tissue PZ can constitute up to 80% of prostate such volume in a case of BPH. The transition zone TZ consists of two lateral prostate lobes 78a, 78b and the periurethral region indicated at 79. As can be understood from FIGS. 2B-3, there are natural barriers around the transition zone tissue TZ, namely, the prostatic urethra 70, the anterior fibromuscular stroma FS, and a fibrous plane 80 between the transition zone TZ and peripheral zone PZ. Another fibrous plane 82 lies between the lobes 78a and 78b. In FIGS. 2A-3, the anterior fibromuscular stroma FS or fibromuscular zone can be seen which is predominantly fibromuscular tissue.
BPH is typically diagnosed when the patient seeks medical treatment complaining of bothersome urinary difficulties. The predominant symptoms of BPH are an increase in frequency and urgency of urination. BPH can also cause urinary retention in the bladder which in turn can lead to lower urinary tract infection (LUTI). In many cases, the LUTI then can ascend into the kidneys and cause chronic pyelonephritis, and can eventually lead to renal insufficiency. BPH also may lead to sexual dysfunction related to sleep disturbance or psychological anxiety caused by severe urinary difficulties. Thus, BPH can significantly alter the quality of life with aging of the male population.
BPH is the result of an imbalance between the continuous production and natural death (apoptosis) of the glandular cells of the prostate. The overproduction of such cells leads to increased prostate size, most significantly in the transition zone TZ which traverses the prostatic urethra (FIG. 3).
In early stage cases of BPH, drug treatments can alleviate the symptoms. For example, alpha-blockers treat BPH by relaxing smooth muscle tissue found in the prostate and the bladder neck, which may allow urine to flow out of the bladder more easily. Such drugs can prove effective until the glandular elements cause overwhelming cell growth in the prostate.
More advanced stages of BPH, however, can only be treated by surgical interventions. A number of methods have been developed using electrosurgical or mechanical extraction of tissue, and thermal ablation or cryoablation of intracapsular prostatic tissue. In many cases, such interventions provide only transient relief, and there often is significant perioperative discomfort and morbidity.
In one prior art ablation method for treating BPH, an RF needle in inserted into the prostate and RF energy is delivered to prostate tissue. In a first aspect of the prior art system and method, the elongated RF needle can be extended from an introducer member into the prostate lobes from the urethra. Some prior art systems further utilize an insulator sleeve extended over the RF needle through the urethral wall to prevent thermal damage to the urethra. The resulting RF treatment thus ablates tissue regions away from the prostatic urethra and purposefully does not target tissue close to and parallel to, the prostatic urethra. The prior art systems and method leave an untreated tissue region around the urethra in which smooth muscle cells and alpha adrenergic receptors are not ablated. Thus, the untreated tissue can continue to compress the urethra and subsequent growth of such undamaged tissue can expand into the outwardly ablated regions.
In another aspect of some prior art RF methods, the application of RF energy typically extends for 2 to 3 minutes or longer which can allow thermal diffusion of the ablation to reach the capsule periphery of the prostate. In some instances, the application of RF energy for such a long duration can cause lesions that extend beyond the prostate and into the urethra. Such prior art RF energy delivery methods may not create a durable effect, since smooth muscle tissue and are not uniformly ablated around the prostatic urethra. Due to the size of lesions created with RF ablation, these prior art systems typically ablate at a suboptimal location within the prostate (e.g., at a distance of 2 cm or greater from the prostatic urethra) to prevent damage to this tissue. The result can be leaving non-ablated tissue adjacent the urethra that may once again be subject to hyperplasia. As a result, the hyperplasia in the lobes can continue resulting in tissue impinging on the urethra thus limiting long term effectiveness of the RF ablation treatment.